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Messages - nooneknows

Closing the back is quite easy, worth a try, although it completely changes the speaker box response, there's an amount of docs about, I'm not even try to simulate it with my speaker design SWs, I don't have the speaker con measures, I'll just try it with cutting a piece of wood ;)


I have the '94 version of the schematic and the layout, I assume you have them, have you already checked any differencefrom this to yours? I don't expect so many differences
BTW, any hint about the speaker too? Any experience with different cones?

I am partial to Jensen C12R and C12K (I had them in my old Peavey Classic 30 and they were both delicious compared to the original mounted, with a preference for the C12K) but I don't know how they sound compared to the one installed in the Eighty Five, which I suppose it could be an Eminence, rebranded.

I finally opened my Eighty Five. Some values are a bit different than the schematics of the Studio 85 I posted, for example C21 is 2n2 and C23 is 560p, the rest seems similar.

Anyway I desoldered C21 and I have to say I solved my problem, the tone of the clean channel is way way nicer and now usable.

I then put a 150pF over C26 and the harsh spikes are gone.

I think I'll stay with this for a while, to get used with the new tone.

thank you all for all the hints, hope this will be useful for other users.
Quote from: willpirkle on April 20, 2022, 08:49:01 AMHave you determined if the brittle-ness is an EQ thing or a lack of Nonlinearity in the input stage?

Not yet since the amp is in my other home, I think I'll check it in a couple of weeks, for sure, I'll try with my old GE7 as you suggested.
thank you!

thanks for the replies.

Looking at the schem again, I will do the C21 lift for sure, it's clearly an high pass at low volume.

I don't think the C25 mod works instead, it's an high pass but I calculated a cut freq of 22 Hz, so enlarging the cap doesn't seem so effective.

verifying the first stage, it seems similar to a VCVS opamp high pass, but I don't understand why the 510KR is not connected to the opamp output but to a resistor network, I'm not able to calculate it. Am I wrong? Any idea?

thank you

Mine is the "Eighty Five", not the Studio 85, I thought it was the same. I haven't opened it yet to check if the schematics I have for the Studio 85 is usable indeed.

BTW, maybe the speaker contributes to the glassy vibe: I have a sidekick 25 reverb too, it was almost unusable until I replaced with a Jensen C10R the original Fender cone, the sound is still a bit boxy but it is way way more nicer and rounder now.

caused by a pure nostalgic wave, I purchased an old fender eighty five, in very good condition.
It was my first amp, back in 89/90 , can't remember exactky. At the time it seemed it was very musical. With my current ears...mmmh, not so much.

Clean channel is beyond brittleness, it's almost a kinfe, dirt channel with gain at 0 is far better but still it sounds 'strange', at least compared to my princeton RI.
85 it's glassy, it's thin. I've noticed that if I connect directly the guitar to the amp in the sound is far better, it's only low (and driy, with no vol control or reverb, ok).

I checked the only schematics I've found, the studio85, I assume it's very similar if not identical.
The clean channell seems not having any real filtering, just like a common fender first tube stage, then the signal is routed directly to the tone control or to an additional  'dirt' stage, much more filtered, it depends on the channel switching.

To me the tone stack , in common with the two channel, seems a lot like a standard fender tone control, I simulated in the response and it's comparable, except a bit attenuated.

Ok, Are there any known mod to bring some warm and or get rid of all this glassyness ?

thank you in advance for your kind help.


I've found the schematic for example here: